This invention relates to dynamoelectric machines and more particularly to a flux shunt for large generators.
In the end turn region of large generators stray magnetic flux, both from the rotor field winding and from the currents flowing in the stator coils, follow undesirable patterns. This stray flux contains axial components, which penetrate the stator end tooth region causing additional losses and heating therein. As ratings and machine sizes have increased, this eddy loss heating has become a serious problem. Historically, the problem was managed in the stator tooth area by slitting the last few inches of the core iron and by stepping the stator core end packs. Recent attempts to provide additional cooling in this area will be satisfactory for existing ratings and machine sizes. Other schemes have utilized flux shields in the tooth portion of the stator core. These are typically copper plates or loops situated directly in front of the stator teeth. These shields are conductive members of low magnetic permeability and arranged to produce circulating currents therein which form a shielding magnetic field diverting the stray currents away from this region of the stator. For high rated machines, the currents induced in these types of shields produce extremely high losses, many times higher than that normally seen in the stator end iron. In most cases, liquid cooling of these shields is required.
Conventional schemes for reducing this type of loss, such as slitting the iron or accepting the loss and adding interlaminar cooling ducts can only be accomplished during the manufacture of the stator core. For machines that have already been built an alternative scheme is required to reduce the adverse effects of stray magnetic flux systems hereinbefore described.